Unmanned aerial vehicles or “drones” are aircraft that may be operated without a human pilot on board—for example, controlled remotely by a human operator or autonomously by onboard computers. Some drones are lifted and propelled by one or more propellers. For example, many drones (e.g., quadcopters) include vertically oriented propellers that enable the drone to be operated above a certain geographical area for use in surveillance, product delivery, aerial photography, agriculture, recreation, scientific research, data collection, and many other applications. One drawback with conventional drones is that their load-carrying capacity and operational time (i.e., airtime or flight time) are limited by the battery life of the drone. Accordingly, there remains a need in the art for methods and systems for improving the load-carrying capacity and operational time of drones, as well as providing other benefits over existing drone technology.